The preparation of block copolymers of mono alkenyl arenes and conjugated dienes is well known. One of the first patents on linear ABA block copolymers made with styrene and butadiene is U.S. Pat. No. 3,149,182. These polymers in turn could be hydrogenated to form more stable block copolymers, such as those described in U.S. Pat. No. 3,595,942 and U.S. Pat. No. Re. 27,145. A number of other variations for block copolymer structures have been found since then. One of the types of block copolymers that has found limited utility in the past have been tetrablock copolymers having the structure ABAB or BABA, where the A block is a styrene block and the B block is a conjugated diene block, typically either an isoprene block or a butadiene block. These polymers in turn have sometimes been hydrogenated. Such tetrablock copolymers are disclosed in a variety of patents, including U.S. Pat. Nos. 4,874,821; 5,378,760; 5,492,967; 5,549,964; 5,554,697; 6,106,011; and 6,239,218.
One of the many end uses for block copolymers and tetrablock copolymers is in fibers and films. See, for example, U.S. Pat. Nos. 5,549,964 and 5,705,556. However, during film and fiber formation, breaks are a common problem for highly elastic rubber compounds. Many of the existing block copolymers and formulations based on such block copolymers continue to have problems with breaks. What is needed is a polymer and compound that possesses enhanced strength to produce tougher films and fibers that are much less likely to break during processing. In addition, highly elastic compounds have a tendency to orient during injection molding in long or complex molds. This orientation leads to warpage and non-uniform shrinkage during de-molding or heating. What is needed then is a material with good elastic properties that can be easily injection molded into a part with isotropic properties. It is also desirable to produce a polymer with a higher modulus thus providing a stiffer rubber. A stiffer, stronger rubber allows the use of less polymer to achieve a desired stretching force, and is therefore, more economical.